This invention relates to variable capacity compressors which compress refrigerant gas primarily adapted for use in air conditioning systems for automotive vehicles, and more particularly to a compressor of this kind which has a control element rotatable in opposite directions in response to the difference between high pressure and low pressure for varying the compression starting timing of the compressor and hence the capacity thereof.
A variable capacity compressor of this kind has been proposed, e.g., by U.S. Ser. No. 196,329, now U.S. Pat. No. 4,813,854, assigned to the present assignee, in which, as shown in FIG. 1, a pair of pressure-working chambers B.sub.1, B.sub.2 are provided at diametrically opposite locations, and a control element A has a pair of integral pressure-receiving protuberances A.sub.1, A.sub.1 slidably received in the pressure-working chambers B.sub.1, B.sub.2 and dividing them into lower-pressure chambers B.sub.1L, B.sub.2L and higher-pressure chambers B.sub.1H, B.sub.2H. The lower-pressure chambers B.sub.1L, B.sub.2L are supplied with suction pressure Ps as low pressure, whereas the higher-pressure chambers B.sub.1H, B.sub.2H are supplied with discharge pressure Pd as high pressure for creating therein control pressure Pc. A control valve device C is operable in response to the suction pressure Ps within a suction chamber I for controlling the control pressure Pc.
In the proposed compressor, when the suction pressure Ps within the suction chamber I is below a predetermined value, the control valve device C is open to leak the control pressure Pc within the higher-pressure chambers B.sub.1H, B.sub.2H into the suction chamber I, whereas when the suction pressure Ps is above the predetermined value, it is closed to keep the control pressure Pc at a high level, whereby the control element A is rotated in response to the difference between the sum of the suction pressure Ps and the urging force of a torsional coiled spring D which urges the control element A toward a partial capacity position, and the control pressure Pc, between two opposite extreme positions, i.e., a full capacity position shown in FIG. 1 and the partial capacity position to be assumed by the control element A when rotated in a clockwise direction as viewed in FIG. 1, thereby varying the timing of commencement of the compression stroke and hence the delivery quantity or capacity of the compressor.
However, according to the proposed compressor, the discharge pressure Pd is introduced through a restriction passage F into one higher-pressure chamber B.sub.1H, wherefrom it is supplied to the other higher-pressure chamber B.sub.2H via a passage E for creating the control pressure Pc within the both higher-pressure chambers B.sub.1H, B.sub.2H. However, the control pressure Pc within the one higher-pressure chamber B.sub.1H is created by the discharge pressure Pd directly supplied to the chamber B.sub.1H through the restriction passage F and thus behaves as dynamic pressure. As a result, when the suction pressure Ps within the suction chamber I is below the predetermined value and the control valve device C is open, the control pressure Pc within the one higher-pressure chamber B.sub.1H is apt to be throttled by the passage E while leaking therethrough. Consequently, the control pressure Pc within the one higher-pressure chamber B.sub.1H is not promptly lowered and accordingly the control element A is not smoothly rotated from the full capacity position to the partial capacity position, resulting in poor controllability of the capacity of the compressor.
Further, even when the control pressure Pc within the higher-pressure chambers B.sub.1H, B.sub.2H decreases to its minimum level, it is still too high with respect to the suction pressure Ps, i.e., there is too large a difference between the control pressure Pc and the suction pressure Ps to obtain a sufficiently wide variable range of the capacity of the compressor.
If the setting load of the torsional coiled spring D is increased in order to enable the control element A to promptly rotate toward the partial capacity position, the urging force of the spring D becomes so large that the control element A does not promptly rotate toward the full capacity position. Besides, the increased setting load of the spring D can lower the safety factor thereof.